The invention relates to a method for providing a DNS (DNS: Domaine name system) server address list from a server to a client, comprising the steps of:
The client requests an IP (IP: Internet protocol) address from the server and the server responses by assigning the IP address together with said DNS address list to the client.
Such a method is known in the art, in particular for systems providing access to the internet or an intranet. Such a system is shown in FIG. 3. The system comprises an ADSL terminal 1, herein after referred to as Mxx (ADSL: Asynchronous digital subscriber line). The terminal 1 is running a DHCP server (DHCP: Dynamic host configuration protocol), herein after referred to just as server and acts like a router or bridge between a client 2 and the internet or intranet. In FIG. 3 the internet or intranet is represented by DNS servers 3 (DNS: Domain name system).
The Mxx makes several DNS servers—being i.e. associated with different networks—available for each client. There might also be a DNS proxy associated with the Mxx. The DNS proxy is not a real DNS server but looks like such a DNS server towards the client. The DNS proxy forwards a DNS request to a real DNS server in the internet or an intranet and forwards the co-ordinated response from said DNS server back to the client.
The operation of such a system partly corresponds to the method described above, wherein a list of DNS server addresses is provided by the server to the client upon request of an IP address.
According to the prior art said list is statically configured, i.e. upon each request the same list in which the DNS server addresses are listed in the same or fix order is provided to the client. Said list may be configured in the client or obtained from the server. Anyway, in the case that the client wants to put a DNS request to the internet or intranet the client looks up the list and starts by asking the first DNS server in the list as to whether it is ready for responding the DNS request. The first server in the list is designated to be the best available DNS server. If the first DNS server in the list does not respond the client goes to the second DNS server in the list and tries to get a response to a DNS request from the second server etc.
However, with statical configuration of the DNS server address list available to the client according to prior art there is the risk that a DNS server is still mentioned first in the list, that means is still being designated as the best available DNS server, although it has gone down in the meantime. In that case the client would nevertheless first ask the DNS server mentioned at the first position in the list although it has already gone down because it has not been removed from the first place in the list. In that way time is lost and the delay time for receiving a response to a DNS request increases for the client due to the statical configuration of the DNS server address list. Moreover, statical configuration of said list can make certain DNS servers overloaded although other DNS servers would be able to respond more quickly.